FIELD BROWN DWARFS FOUND BY DENIS

We present three candidate field brown dwarfs, identified by the DENIS survey. This on-going three colour survey of the southern sky has, as of July 1997, covered over 30% of the southern hemisphere in the I, J and K-short passbands. The enormous sampled volume makes DENIS ideal for detecting brown dwarfs. The present results are based on prelimina ry processing of about 230 square degrees of DENIS data - a small frac tion of the existing sky coverage. This reveals a sizeable population of very cold dwarfs, three of which are at least as cool as GD 165B. I nfrared spectra confirm their dwarf status, and provide effective temp erature information: one object (DENIS-P J1058.7-1548) is comparable i n temperature to GD 165B and a second (DENIS-P J1228.2-1547) is slight ly cooler, while a third (DENIS-P J0205.4-1159) is significantly so - though not as cold as GI 229B. The infrared spectrum of DENIS-P J0205. 4-1159 shows evidence for a methane absorption band, which implies an effective temperature much below the stellar limit. Lastly, recent det ections of lithium in DENIS-P J1228.2-1547 have proven it to have a su bstellar mass. This makes it (together with the recently discovered ob ject Kelu-1) the first bona-fide isolated field brown dwarf.